1. Field of the Invention
Embodiments of the present disclosure pertain to centralizers and, in particular, to a centralizer having a body formed from two materials, one arranged within an inner part of the body and one arranged in an outer part of the body.
2. Description of the Related Art
Currently available centralizers are manufactured from a single material, generally a plastic material. The material is injected on the tubular element to be centralized, more specifically on a both hollow and solid pumping rod. The material may be further arranged by employing a two-piece fitting joint or it assembly by other mechanisms.
In those cases where the material is injected on the tubular element, a centralizer is obtained that has a molecular framework and an attachment level to the tubular element that varies significantly on the basis of the injecting conditions. However, under normal production conditions, the molecular framework of the centralizer can be adjusted to be as crystalline as possible, increasing the attachment to the tubular element. Generally, either surface modification (such as sandblasting) or slot machining may be used for improving attachment of the centralizer to the tubular element.
When the centralizer is arranged by assembling multiple pieces, the attachment is much weaker than using injection. Even more, some additional insertions may be added, such as pivots, screws, etc. to allow for positioning of the parts. On the other hand, assembling centralizers is advantageous because they can be more easily fitted in either position which may be desired.
Regarding the material properties of these centralizers, the plastic is generally highly hard and resistant to deterioration and corrosion. Engineered polymers are those which meet the requirements to operate in oil wells. The most popular engineered polymers include polyphenylene sulfide (PPS), high temperature polyamides (PA), polyphthalamide (PPA), polyphenylene ether (PPE).
These engineered polymers may be further modified by aggregates such as glass, minerals, or aramid fibers. Ceramic enhancers may be employed for maintaining mechanical properties at high temperatures. While the base polymers provide chemical resistance during use, the enhancing elements provide resistance to creep (“creep resistance”). The resulting composite material improves the properties of the base polymer, which may be beneficial to ensure the expected performance in very hard environments.
Although these materials have shown excellent performance in aggressive environments, they are expensive and may cause deterioration of the metallic piece against which they move. For example, metallic damage due to the employment of a PPS centralizer in some oil wells has been reported. The presence of glass fibers as enhancer in the above mentioned centralizer has increased erosion and damage of the metallic surface, and has resulted in significant thickness reduction. Furthermore, long term contact with high temperature environments that also deteriorates the mechanical properties of these materials, resulting in detachment.
It may be assumed that each possibility of having a single material for manufacturing a centralizer has a clear disadvantage and a related problem as well, which in the end causes early extraction and replacement of the piece. Documents US 2006/231250, U.S. Pat. No. 6,585,043, WO 98/50669, CA 2101677, U.S. Pat. No. 3,963,075, RU 2211911, US 2005/0241822, US 2004/0112592, US 2003/0070803, U.S. Pat. Nos. 4,793,412, 7,156,171, 7,182,131, 7,140,432 and 6,484,803 disclose centralizers made from a single material, including rollers or blades.
From the forgoing, then, it may be understood that there is an ongoing need for improved centralizers.